access GPSD port 2947 over network

Question

Have a RPI2 with latest Jessie Lite Raspbian Jan 2017 with Adafruit Ultimate GPS hat and PPS using info from a post at digitalbarbedwire.com. Easy setup and PPS and all gps commands work great locally.

I am trying to get gpsd to accept incoming requests over the network on port 2947 to export position info (OpenCPN). I edited /etc/default/gpsd to add the -G option GPSD_OPTIONS="-n -G" but external requests are not being allowed. If I stop gpsd (sudo service stop gpsd), and invoke gps in the foreground (/usr/sbin/gpsd -N -n -G /dev/ttyAMA0 /dev/pps0, all works fine! So I am guessing there is a permissions problem starting the gpsd as a daemon, but I haven't figured it out yet. Drivings me nuts!

Any suggestions?

Relevant files:

$ cat /lib/systemd/system/gpsd.socket
[Unit]
Description=GPS (Global Positioning System) Daemon Sockets

[Socket]
ListenStream=/var/run/gpsd.sock
ListenStream=[::1]:2947
ListenStream=0.0.0.1:2947
SocketMode=0600

[Install]
WantedBy=socket

$ cat /etc/default/gpsd
# Default settings for the gpsd init script and the hotplug wrapper.

# Start the gpsd daemon automatically at boot time
START_DAEMON="true"

# Use USB hotplugging to add new USB devices automatically to the daemon
USBAUTO="true"


# Devices gpsd should collect to at boot time.
# They need to be read/writeable, either by user gpsd or the group dialout.
DEVICES="/dev/ttyAMA0 /dev/pps0"

# Other options you want to pass to gpsd
GPSD_OPTIONS="-n"

$ cat /lib/systemd/system/gpsd.service
[Unit]
Description=GPS (Global Positioning System) Daemon
Requires=gpsd.socket
# Needed with chrony SOCK refclock
After=chronyd.service

[Service]
EnvironmentFile=-/etc/default/gpsd
ExecStart=/usr/sbin/gpsd -N -G $GPSD_OPTIONS $DEVICES

[Install]
Also=gpsd.socket

Any ideas?

Answer 1

Gpsd is not actually listening on port 2947, systemd is. By default in Debian this is local only. When a request comes in systemd starts gpsd, if necessary, and redirects future requests to the daemon. So giving gpsd the -G parameter will not actually change anything.

You need to add an override for the systemd gpsd.socket unit, and tell it to listen on all addresses:

# /etc/systemd/system/gpsd.socket.d/socket.conf
[Socket]
# First blank ListenStream clears the system defaults
ListenStream=
ListenStream=2947
ListenStream=/var/run/gpsd.sock

Best practice is to put this override file in /etc/systemd/, and not to edit the unit files in /lib/systemd/.

Documentation on the systemd.socket syntax: https://www.freedesktop.org/software/systemd/man/systemd.socket.html